ASoC: cs35l41: Document CS35l41 External Boost

Document internal and external boost feature for ASoC CS35L41.
For internal boost the following properties are required:
- cirrus,boost-peak-milliamp
- cirrus,boost-ind-nanohenry
- cirrus,boost-cap-microfarad

For external boost, the GPIO1 must be configured as output,
so the following properties are required:
- cirrus,gpio1-src-select = <1>
- cirrus,gpio1-output-enable

Signed-off-by: David Rhodes <drhodes@opensource.cirrus.com>
Signed-off-by: Lucas Tanure <tanureal@opensource.cirrus.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220413083728.10730-16-tanureal@opensource.cirrus.com


Signed-off-by: Takashi Iwai <tiwai@suse.de>